This invention relates to a plural motor fan system. More particularly, the invention relates to speed control of a two motor fan system useful for moving air through a heat exchanger in a motor vehicle engine cooling system, in which each motor drives a respective set of fan blades at more than one selectable speed.
In cooling systems for motor vehicles, it is known to provide a dual fan assembly, each fan being mounted on a respective shaft of a separate direct-current ("DC") motor. The motors are independently connected to their power source. Each such motor includes only a single armature coil winding, and drives a shaft which is mechanically unconnected to that driven by the other motor. Each fan rotates at a rate corresponding to the speed of the motor which is driving the shaft connecting to the fan. Different combinations of motor speed may be selectively chosen to suit the application environment. For instance, both motors may operate at a high speed, or low speed; it is not necessary that the high speed of the two motors be equal, or that the low speed of the two motors be equal.
To vary the speed of the motors in such a system, it has been known to vary the voltage that is applied to each motor with external conventional means, which can provide a selectable voltage drop from a power source. The external means can be constructed with conventional electronic parts or resistors. But the bulk of such external means creates packaging difficulties for it must be packaged separately. Also, the component cost of the external means adds to system cost; additionally, power conversion is made less efficient by such conventional external means; the connection between the motor and the external power source is also made more complex. Where the external means uses a resistor, problems relating to intrinsic characteristics of resistors cause certain disadvantages. Resistors, by nature, operate at extremely high temperature; resistors have shown a low reliability in a motor vehicle environment; and resistors are inefficient as power is wastefully dissipated. Also, in such a system, because the two motors are electrically independent of each other, a separate means for radio frequency interference suppression is required for each motor.
Alternatively, to vary the speed of the motors in such a system, it has also been known to include a selectably connected resistor internal to each motor. That arrangement presents packaging difficulties associated with the internal resistor and with the additional heat that is dissipated internally. The disadvantages intrinsic to the use of resistors as noted above are also a problem. And separate means for radio frequency suppression are still required.
Another type of plural motor fan system in the prior art for moving air through a heat exchanger in a motor vehicle cooling system connects two motors, each still including only a single armature coil winding, electrically in series with each other, to obtain a respective motor speed slower than that of the same motor when the external applied voltage is applied in full across each motor's armature coil winding. That system, however, provides an inflexible low to high speed ratio for each motor. If two such equal windings in similar motors are placed in series driving equal loads, then one-half of the total applied voltage is dropped across each motor. Attempts to adjust the voltage drop of one motor to affect the performance of the other motor will have a detrimental effect on the system when both motors run in parallel. Given a constant designed total motor power in the parallel mode, maximized low speed power is obtained with equal power motors. Even so, with one-half voltage on a fan system, the fan power is reduced to a generally unsuitably low power level for automotive applications. Attempts to use unequal power motors would cause the respective power differences between the two motors to be reversed when changing between series and parallel operation. Furthermore, that would cause a reduction of the low speed total power with respect to total high speed power. A desirable low speed voltage for each motor would be one that is equal to that of each other and also intermediate of the full and half value of the voltage supplied by the motor vehicle.
Furthermore, a minimum of three switches (e.g., SPST relays) are required to implement that prior art system; and separate switches are required which lead into each motor, thus complicating the prior art system's electrical connection. It is also not possible in that system to have one motor running at its high speed while the other is running at its low speed.
In the motor art generally, it has been known to construct a dual wind two speed motor by winding two armature coil windings on a common rotor, and to selectively switch between a connection including both armature coil windings in series to obtain a low motor speed, and a connection including just one armature coil winding to obtain a higher motor speed. One such motor disclosed in commonly assigned U.S. Pat. No. 4,910,790, Mar. 20, 1990. Similarly, the following references each discloses a motor of that type: (1) Published British Patent Application No. 2,041,677; and (2) French Patent No. 2,122,132.
Though no prior art plural motor fan system for motor vehicles is heretofore known which includes two separate dual wind two speed motors which independently drive a respective set of fan blades, such a system would nevertheless have numerous disadvantages. With two such dual wind motors driving respective loads, the number of motor parts is duplicative and the cost is high, as each motor is a complete multi-speed motor in itself. There is still a need to provide a two motor assembly for driving two fan blades to move air through a heat exchanger for an automotive engine which does not suffer from one or more of the disadvantages noted above.
It is an object of the present invention to provide a two motor assembly which will fulfill the above-described need. In accordance with the principles of the present invention, this objective is achieved by providing a two motor assembly of the type described which includes a first two speed DC motor of the type having a first fixed magnetic field and an armature rotor rotatable to drive first fan blades. A multiplicity of armature coil turns are provided on the armature rotor along with a commutator assembly which is electrically connected with the multiplicity of armature coil turns. A plurality of brushes including a tap brush cooperate with the commutator assembly to alternatively operate the plural speed DC motor (1) in a first speed mode wherein (A) a system voltage is applied across all of the multiplicity of armature coil turns to produce a net total back electro-motive force and armature reaction interacting with the first magnetic field to cause the armature rotor to rotate in the first speed mode and (B) a tap voltage intermediate the system voltage reduced across a predetermined number of armature coil turns less than all of the multiplicity of armature coil turns is provided through the tap brush and (2) a different second speed mode. A second DC motor is provided which includes a rotor for driving second fan blades and cooperating field and armature coils for rotating the rotor. Circuitry is provided for alternatively (1) applying the tap voltage across the armature coils of the second DC motor so as to operate the second DC motor in a first speed mode when the first two speed DC motor is operated in the first speed mode thereof and (2) applying a system voltage across the armature coils of the second DC motor so as to operate the second DC motor in a second speed mode when the first two speed DC motor is operated in the second speed mode.
Another object of the present invention is the provision of a fan system for use in moving air through a heat exchanger for an automotive engine which includes a shroud adapted to be operatively associated with the heat exchanger so as to receive air after it has passed through the heat exchanger. The shroud has discharge openings therein for allowing air received therein which has passed through the heat exchanger to be discharged therefrom. First and second fan blades are rotatably mounted within the shroud to effect a flow of air into the shroud through the heat exchanger and a flow of air out of the shroud through the discharge openings and a two motor assembly of the type previously described is provided for driving the first and second fan blades.
Preferably, the second motor is a simple one speed DC electric motor and the circuitry is simplified to include only two switches, which are capable of operating the two motors together alternatively in their first speed modes or their second speed modes. However, the arrangement permits other different mode operations where the shroud which associates the fan blades with the heat exchanger provides separate flow paths for each motor and fan blade combination.
The invention also contemplates the utilization of a second similar two speed DC motor as the second motor in which case it becomes possible to provide each motor with three operating speed modes rather than two and many more where separate shroud paths are provided.
Another object of the present invention is the provision of a two motor system of the type described which is simple in construction, effective in operation, and economical to manufacture and maintain.
These and other objects of the present invention will become more apparent during the course of the following detailed description and appended claims.